Methods and computer programs have been developed in this laboratory which allow the accurate ab initio calculation of the ground and excited state properties of molecules of some size. It is proposed that these be applied to the calculation of the circular dichroism spectra of a number of chromophoric groups whose excited electronic states are important to a number of biological processes. In particular, the understanding of photochemical reactions requires the assignment and full knowledge of the excited electronic states reached by the absorption of light. An example is the photochemical conversion of ergosterol to vitamin D. Ergosterol is a steroid containing a diene group in the B ring which is responsible for the primary absorption of electromagnetic radiation. Experimental circular dichroism spectra in the vacuum UV have become available to 140 nm. Theoretical calculations, coupled with this data, should yield considerable new information on the excited states to be studied and their circular dichroism. The compounds to be examined are a carbonyl, (plus) 3-methylpentanone, trans cyclooctene, an as yet unspecified conjugated, optically active diene, the smallest cyclic hydrocarbon, cyclopropane and its di-methyl derivative and the other linkage. All of these molecules are or will be of fair conformational rigidity so that undue averaging over nuclear motion will not be necessary to evaluate the circular dichroism. A spin off benefit of these studies will be the further development of ab initio theoretical methods for dealing with molecules of this size.